This application claims priority under 35 USC 119 to Japanese Application No. 11-360936, filed Dec. 20, 1999, and Japanese Application No. 11-362259, filed Dec. 21, 1999.
1. Field of the Invention
This invention relates to a solid-liquid filtering method and system for sewage, waste water and the like.
2. Prior Art
According to a conventional solid-liquid filtering process, solid containing liquid has been filtered off through porous filter media such as woven fabric, gauze or mesh, knitted fabric, penetrable membrane and the like. Liquid to be filtered is passed through a filter medium from one side to be other side thereof by loading, pressing, evacuating, centrifuging and the like, thereby solid being captured by pores if the solid particle is Larger than the pore size.
In the conventional system for conducting the above-mentioned filtering process, the liquid is basically forced to pass through a filter from one side to the other. Average solid particle size in the liquid varies depending on kinds of liquid to be filtered while each filter medium has its inherent pore size fallen in a certain range. When the liquid contains solid of various particle sizes, it is necessary to change filter media with an increase or decrease in the particle size. Further, the liquid to be filtered is restricted by a specific filtering system if its filter medium is not changed, which inconveniently reduced applicability of the filtering system.
Filtered solid particles are gradually accumulated on the filter media with the elapse of filtering process to cause clogging of the filter. Such a clogging situation decreases the filtering effect and finally halts filtration. As the liquid is forced to pass through the filter media as described above, solid is strongly captured by filter pores. The finer the solid particle becomes, the more frequently such clogging occurred.
It is not economical, efficient nor practical from an operational standpoint to use a filter medium to its filtering capacity because such a medium is no longer reusable. For that reason, clogged filter media are usually washed to remove filtered off solid particles and reused repeatedly. In order to solve problems caused by clogging, a fixed filter medium is subjected to so-called back washing by forcibly passing wash-water through the medium in the backward direction, or clogged solid particles are forcibly blown offer sucked out by means of a conventional device.
Although back-washing is a simple and convenient treatment for clogging, such a treatment should be conducted at a high water pressure by using a large amount of water for a long period of time when pore size of the filter medium is considerably small, or when solid particles are excessively fine or adhere strongly to the medium. The filter medium is sometimes used continuously even under an inefficient condition as described above, or a washing period should be shortened unavoidably.
On the other hand, an application of a specific device for washing would increase the production cost and decrease the operational efficiency.
According to the present invention, it is possible to filter off solid of normal to superfine particles through a novel type of filter media which can be easily and completely washed by conventional back-washing. The present invention provides a novel solid-liquid filtering method and system which exceeds the conventional concept of filtration.
An object of the present invention is to provide a solid-liquid filtering method in which liquid to be filtered is passed through a thick band of assembled filaments to filter off and capture solid by supplying liquid in the direction of filament retainment, said band comprising closely paralleled monofilaments of predetermined length, one end portion of which being fixed and the other end portion being floated so as to keep said band in a plane situation at proper location by a support only when each filament is forced to turn in a regular direction.
Another object of the present invention is to provide a solid-liquid filtering means which comprises a thick band of assembled filaments prepared by closely arranging paralleled monofilaments of predetermined length, a means for fixing one end portion of said band and a network support for keeping said band in a plane situation at proper location when said band is forced to turn in a regular direction, one end portion ef said monofilaments being fixed and the other end portion being floated.